The field of which this invention is a part is synthetic resin coating compositions, particularly powder coating compositions.
Coatings formed from organic powders, the so-called powder coatings, are gaining acceptance in the industry. Advantages of powder coatings are the elimination of solvents and the potential 100% utilization of the powder, both of which afford a practical means to abate air pollution in paint processing.
Power coatings, as conventionally made, are generally limited to a single color composition. In the process for making powder coatings, e.g., the melt blend process, the fusible resin is melted and mixed with one or more pigments and other additives. The melt mix is then cooled and processed to a fine powder. Each particle of the powder, even though a number of pigments may have been used, will be the same color as all the other particles. When applied, heated and fused to a coating, an even color is obtained. Two powders, each of which contain different colored pigments, if intimately mixed, will produce a coating hich is substantially monocolored. If the powders are quite different in particle size and the resin components have quite different melt viscosities, then some multicolored effect will be obtained. However, with such systems, the coating itself will be inferior, due to the non-homogeniety of the film forming resins.
In U.S. Pat. No. 3,095,400, a method is proposed for making plastic compositions having a speckled appearance. According to the patent, ordinary colorants, such as pigments and dyes, are generally not suitable for producing speckled effects. Most colorants are supplied in the form of finely ground powders with particle sizes of about 365 mesh or smaller. Particles below about 200 mesh in size are not readily discernible as discrete particles but rather tend to alter the color of the material in which they are incorporated. The use of ordinary colored particles of a size greater than 200 mesh results in the disintegration of the particle during processing of the base material. This causes undesirable effects such as uncontrollable smearing and discoloration of the base material by the disintegrated particle. These difficulties are overcome by incorporating a colored thermosetting resin in with a thermoplastic resin to obtain the colored effect. As described by the patent, the particle size of the pigmented thermoset resin is quite large, being larger than 200 mesh and preferably larger than 80 mesh but smaller than 10 mesh. Sucn compositions are useful in molding compounds, but are too large to be used successfully in powder coatings.
In U.S. Pat. No. 3,049,761, multicolored sheet material is made by blending granulated resin of various colors with a plastisol paste. The mixture is then formed into a layer or sheet, fused and pressed.
In U.S. Pat. Nos. 2,837,437, 3,415,673, 3,487,041, 3,536,658 and 3,663,493, the use of pigments and dyes with various polymers to produce even colored compositions is described. U.S. Pat. Nos. 2,097,233 and 3,108,893 describe methods for applying coatings in patterns using electrostatic techniques.
In U.S. Pat. No. 3,725,089, a method for making multicolored coatings using aqueous dispersions is described.